Why do elements within a group (family or column) in the Periodic Table exhibit similar chemical behavior?
A They all have the same number of protons.
B Within a group, the atoms are the same size.
C The number of electrons in their outermost shells is the same.
D All of the above.
No. Write (or look up the electron configuration) for say the group I elements.
You KNOW it can't be a because every element has a different number of protons. That also tells you it can't be D. You KNOW elements are not the same size so it can't be B.